# What crosses the boundary

> @faustine-ai/browser-sandbox documentation · https://browser-sandbox.faustine.ai/docs/boundary/ · source: README.md on GitHub (https://github.com/faustine-ai/browser-sandbox)

Everything between your page and the worker travels by **structured
clone** through a `MessageChannel`. That decides what can and cannot pass:

| Passes | Fails (on the side that tries) |
|---|---|
| JSON values, `Date`, `RegExp`, `Map`, `Set`, typed arrays, `BigInt` | functions and closures |
| `File`, `Blob` (by reference to the same bytes, no copy) | DOM nodes, `Window`, `Response` |
| `ArrayBuffer` (copied) | class instances (arrive as plain objects, methods gone) |
| plain objects and arrays, nested | `Proxy`, `WeakMap`, `SharedArrayBuffer` |

A function returning something unclonable makes that call reject with
`CloneError`; a run returning one ends with `CloneError`. Nothing crosses
partially.